The present invention relates to an electro-acoustic micro-transducer having a three-mode reproduction feature, and more particularly to an electro-acoustic micro-transducer having a high power, high efficiency acoustic transducing feature and a three-mode broad band frequency reproduction feature on a micro-scale basis in a compact electronic appliance, in which part of a yoke is cut out and simultaneously a soft material is used as edges of the incised yoke so that a moving coil assembly can be sufficiently vibrated up and down.
In general, an acoustic reproduction apparatus is classified into a horn type speaker, a system speaker which is used for a hifi audio system such as a component system, including a woofer, mid-ranger and tweeter covering a respectively particular frequency band, a general speaker covering all frequency bands via a single unit, a micro-speaker having an ultra-light and ultra-slim structure which is used in a compact electronic appliance such as a ultra-compact camcorder and walkman, a receiver used for a mobile communications terminal, an earphone having a structure whose part is inserted into the ear, and a buzzer for reproducing only a frequency of a particular band.
In a conventional general speaker, a bobbin around which voice coils are wound is positioned in a magnetic circuit in which a single magnet is installed in a yoke and a top plate is installed on top of the magnet. Also, the upper portion of the bobbin has a structure where the outer circumferential portion thereof is fixed to the upper and lower portion of a frame, the center portion thereof is fixed to a circularly perforated vibration plate and damper, and a center cap called a dust cap for closing the whole of the bobbin is combined in the center portion of the vibration plate.
However, a micro-speaker used in a mobile phone, a camcorder, a notebook PC, an ultra-compact cassette recorder, adopts an electro-dynamic type structure in which a damper is omitted and simultaneously the height of a frame portion is lowered so as to accomplish an ultra-compact and ultra-thin type structure in correspondence to compactness of a set.
In the electro-dynamic speaker as shown in FIG. 1a, a protector 1 is covered on the upper end of a groove type frame 2, a terminal plate 9 is fixed to one side on the bottom surface of the frame 2, and a magnetic circuit is formed of a yoke 8 fixed in the center portion of the frame bottom, a permanent magnet 6 and a plate which are coupled in the yoke 8. A moving coil 5 fixed to a vibration plate 3 is fixed to an edge 4 of the vibration plate 3 formed in the intermediate step portion of the frame 2, so as to be moved in a magnetic gap G between the yoke 8 and the plate 7. In FIG. 1a, a reference numeral 10 denotes an air ventilation hole and a reference numeral 11 denotes a signal lead wire.
The electro-dynamic micro-speaker has a structure for generating an acoustic sound in correspondence to a driving signal created by the up-and-down vibration of the vibration plate 3 and the moving coil 5 due to an attractive and repulsive force which is created by an interaction of a non-alternating (direct-current) magnetic flux generated from a fixed magnetic circuit and an alternating (alternating-current) rotating magnetic flux generated from the moving coil 5 which can move up and down in accordance with the Fleming""s left-hand rule.
However, in the case of the electro-dynamic micro-speaker shown in FIG. 1a, it is not possible to perform an extensive reproduction of a low level sound and a high level sound which are required in the portable electronic appliance in view of a speaker structure when the electro-dynamic micro-speaker is manufactured into an ultra-micro-speaker for use in a camcorder, a notebook PC, a compact cassette recorder and an information communications portable terminal, for the following reasons.
For example, in the case that a speaker is 4 mm in height and 20 mm in diameter as shown in FIG. 1c, a bobbin 4 is set about 2.3 mm in length l and 9.5 mm in diameter. In this case, the whole length l of the bobbin is constructed so that a connection area a, a coil winding area b and a margin c between the coil 5 and a flexible wire 11 are allocated into 0.9 mm, 1.2 mm and 0.2 mm, respectively.
However, in the case that the flexible wire 11 of 0.8 mm in diameter is soldered with the coil 5 by a soldering lead, a vibration width d which makes a coil assembly 15 vibrate up and down is set 0.3-0.4 mm or so which is a distance between the flexible wire 11 and the upper end of the yoke 8.
If the coil assembly 15 vibrates with the set vibration width d or wider, the soldering portion 16 of the flexible wire 11 contacts the upper end of the yoke 8, to thereby cause so we call touch noise generated and lose the value of an acoustic reproduction product.
Thus, although there is a clearance of at least 0.7 mm between the lower end of the bobbin 4 and the bottom of the yoke 8 which can be increased according to the height of a permanent magnet 6 in the conventional art, an extension of a magnetic gap G lowers an efficiency of the speaker greatly. Accordingly, such an extension of the magnetic gap G has not been used.
The vibration width d cannot but limit an allowable input and the size of a magnet used is limited due to the limited vibration width d. As a result, it has not been possible to realize a high power and high efficiency speaker in view of its structure. Further, since a soft material has not been used for an edge of the vibration plate 3 in order to suppress a smooth vibration of the coil assembly 15, it has been difficult to lower a low band resonance frequency f0 of the speaker in proportion to the stiffness of the edge.
Further, when the flexible wire 11 is used in order to supply a driving signal to the moving coil 5 from an external source, both ends of the flexible wire 11 is tightly fixed by a solid bonding material 12 and 13 and the intermediate portion of the flexible wire 11 is fixed to a vibration plate 3 by use of a soft bonding material 14 as shown in FIGS. 1a through 1c. However, when an excessive input signal is applied, the flexible wire 11 may be cut due to overheat.
For reference, in a commercially available receiver product, a rating input is 0.01-0.1 W in the case of a product having 20 mm or less in diameter, 0.2-0.5 W in the case of a product having 36 mm or so in diameter, and 0.5-1 W in the case of a product having 50-57 mm or less in diameter.
Also, in a high quality of a micro-speaker, a rating input is 0.2-0.3 W and the maximum input is 0.5 W in the case of a product having 20 mm in diameter.
As described above, as the size of the speaker grows smaller, a number of structural restrictions are caused. As a result, a low band resonance frequency f0 becomes high and its efficiency and output are lowered.
Meanwhile, an electromagnetic speaker made using an electro-acoustic transducing theory and structure uses only a function of a buzzer for reproducing only a monotonous sound signal of 1 or 2 KHz, which is extremely narrow in actual applications.
For the above reasons, an ultra-compact speaker should appear soon in which a high efficiency multifunction of performing a broad band acoustic reproduction and receiving a large-scale input with an ultra-compact design can be integrated into a single unit in order to realize a compact personal information processing terminal where video, audio and office processing functions are integrated.
To solve the above-mentioned problems involved in the conventional electro-acoustic micro-transducer, it is an object of the present invention to provide an electro-acoustic micro-transducer having a three-mode broad band frequency reproduction feature, which can cover all acoustic reproduction functions of a buzzer, a receiver and a micro-speaker for a portable electronic device, with a single unit in which part of a yoke opposing a soldering portion between a flexible wire and a coil is cut out and simultaneously a soft material is used as edges of the incised yoke so that a coil assembly can be sufficiently vibrated up and down.
It is another object of the present invention to provide an electro-acoustic micro-transducer having a high power, high efficiency acoustic reproduction feature in which a coil assembly is not influenced by an allowable vibration width and a large-scale input is accepted.
It is still another object of the present invention to provide an electro-acoustic micro-transducer having a flat frequency characteristic over all reproduction frequency bands, by using a vibration diaphragm integrated with a reinforcing body.
It is yet another object of the invention is to provide an electro-acoustic micro-transducer having a structure in which a coil assembly and a frame assembly can be simply made, a coupling between a coil and a PCB is simple, and an excessive vibration can be sufficiently absorbed.
It is a further object of the present invention is to provide an electro-acoustic micro-transducer in which a rectangular flexible PCB having a pair of electrode patterns in order to solder both ends of the coil and a flexible wire is rolled and the rolled PCB is used as a bobbin.
To accomplish the above object, in accordance with one aspect, the present invention provides an electro-acoustic micro-transducer comprising: a yoke formed of an internal groove and a vertical incision portion for removing a predetermined vertical wall at at least one side surface; a permanent magnet installed in the groove of the yoke, for generating a non-alternating magnetic field; a plate mounted on the upper surface of the permanent magnet, for forming a magnetic gap between the outer circumferential surface and the upper end of the yoke; a coil wound on a bobbin, which generates an alternating magnetic field when an electric drive signal is externally applied via first and second lead wires and is disposed in the magnetic gap to be displaced up and down according to an interaction with a non-alternating magnetic field generated from the permanent magnet; a cylindrical frame in which the outer circumferential portion surrounds the yoke at the state where the yoke is set to be positioned in the center, the outer circumferential portion is perpendicularly extensively formed in such a manner that a groove is formed therein and an externally communicating throughhole is formed in the groove corresponding to the incision portion of the yoke; and a vibration diaphragm in which the bobbin is supported and the outer circumferential portion is supported in the upper end of the frame, for generating an acoustic sound in correspondence to the drive signal when the bobbin is displaced up and down, wherein spaces in the incision portion of the yoke and the frame are formed of a magnitude of preventing a connection portion between the coil and lead wire from contacting the bobbin during vertical vibration, to thereby extend an up-and-down vibration width of the bobbin.
Here, in the case that the bobbin is rectangularly formed, where first and second band type electrode patterns are lengthily separated and formed on the upper end of the bobbin and a flexible PCB substrate where a coil winding bonding material coating area is located is cylindrically molded and formed on the lower end thereof, both ends of the coil are connected to one end of each electrode pattern, the first and second lead wires are connected to the other end of each electrode pattern, and a single incision portion formed in the yoke is formed opposing the connection portion between the lead wires and the electrode pattern.
Here, in the case that the bobbin is rectangularly formed, where first and second band type electrode patterns are lengthily separated and formed on the upper end of the bobbin and a flexible PCB substrate where a coil winding bonding material coating area is located is cylindrically molded and formed on the lower end thereof, both ends of the coil are connected to one end of each electrode pattern, the first and second lead wires are connected to an opposing position of each electrode pattern with respect to the center of the bobbin, and first and second incision portions formed in the yoke are formed opposing the first and second connection portions between the lead wires and the electrode pattern.
Also, the flexible PCB substrate further comprises third and fourth band type electrode patterns electrically connected with the first and second band type electrode patterns in the inner side surface, for compensating for a linearity of DC magnetic field generated from the permanent magnet.
Further, the frame further comprises first and second guiders for molding the first and second lead wires withdrawn from the coil externally via each throughhole in zigzag form; and an electrode terminal plate in which the first and second lead wires withdrawn via each guider are connected to the lower surface of the frame in either side of the throughhole and first and second electrode pads via which drive signals are applied externally are separately formed, wherein the first and second guiders are removed at the state where the other ends of the first and second lead wires are fixed to the first and second electrode pads.
The vibration diaphragm comprises a body extended from a neck portion on which the bobbin is attached to an outer end in cone shape; a dust cap of a dome shape formed in the neck portion; a rib continuously protruded at a predetermined width and height from the center of the dust cap to the outer end of the body; and an edge for supporting the body to the frame, wherein the body, the dust cap, the rib and the edge are integrally formed.
The vibration diaphragm is formed in the same shape as those of the body and dust cap, and further comprises a reinforcing body attached to the lower end of the vibration diaphragm, having a hole corresponding to the center portion of the dust cap, for reducing a non-linear distortion of the vibration diaphragm.
Also, the vibration diaphragm is comprised of a separable body and an edge.
Meanwhile, the yoke and the frame can be integrated by a quality of a material in a magnetic path.
The electro-acoustic micro-transducer according to the present invention comprises a plurality of sound output holes and a cover plate combined in the lower end of the frame, for preventing foreign matter from entering the frame.
To accomplish the above object, in accordance with another aspect, the present invention provides an electro-acoustic micro-transducer comprising: a yoke formed of an internal circular groove and first and second vertical incision portions for removing a predetermined vertical wall at either side surface; a permanent magnet installed in the groove of the yoke, for generating a non-alternating magnetic field; a plate mounted on the upper surface of the permanent magnet, for forming a magnetic gap between the outer circumferential surface and the upper end of the yoke; a coil wound on a bobbin, which generates an alternating magnetic field when a drive signal is applied and is disposed in the magnetic gap to be displaced up and down according to an interaction with a non-alternating magnetic field generated from the permanent magnet; a cylindrical frame in which the outer circumferential portion surrounds the yoke at the state where the yoke is set to be positioned in the center, the outer circumferential portion is perpendicularly extensively formed in such a manner that a groove is formed therein and first and second externally communicating throughholes are formed in the first and second groove spaces opposing the incision portion of the yoke; and a vibration diaphragm in which the bobbin is supported and the outer circumferential portion is supported in the upper end of the frame, for generating an acoustic sound in correspondence to the drive signal when the bobbin is displaced up and down, wherein first and second spaces respectively formed by the first and second incision portions and the first and second groove spaces are formed of a magnitude of preventing first and second connection portions of the first and second flexible wires fixed to the bobbin from contacting the yoke and the frame during vertical vibration of the bobbin, in order to apply the drive signal externally, to thereby extend an up-and-down vibration width of the bobbin.
The electro-acoustic micro-transducer according to the present invention is applied to an ultra-compact and ultra-thin product.
The present invention can obtain a sufficiently allowable vibration width of the coil assembly by the cutting of the yoke, which makes the edge made of a soft material. Thus, a low level resonance frequency is lowered, to thereby obtain an acoustic reproduction capability of a broad band range in which all functions of a buzzer, a receiver and a micro-speaker are integrated.
Also, the present invention uses flexible wires via an incision portion by the cutting of the yoke to thereby very simply connect between the coil and the electrode terminal plate. As a result, a wire cut problem can be solved and a high withstand input can be accepted, to provide a new speaker structure having a high power and high efficiency feature.
Thus, the present invention can realize a personal information processing terminal in which all functions of video, audio and office processing are integrated.